1. Field of the Invention
This invention generally relates to cells derived from adipose tissue, and more particularly, to adipo-derived stem cells, methods of using adipo-derived stem cells, compositions containing adipo-derived stem cells, and systems for preparing and using adipo-derived stem cells.
2. Description of the Related Art
Regenerative medicine can be defined as harnessing the body's regenerative mechanisms in a clinically targeted manner, using them in ways that are not part of the normal healing mechanism or by artificially amplifying normal mechanisms. One classic example of this process is found in bone marrow transplantation where hematopoietic stem and progenitor cells are harvested from a donor and placed into a recipient in whom the normal hematopoietic regenerative mechanisms have been ablated or substantially depleted or impaired, thereby replacing or regenerating the blood-forming capacity of the recipient (Thomas 1994). In recent clinical and pre-clinical studies this approach has been extended to the non-hematopoietic stem cell component of bone marrow with studies regenerating (or attempting to regenerate) tissues including bone (Connolly 1998; Horwitz, Prockop et al. 1999; Horwitz, Prockop et al. 2001), heart (Fukuda 2001; Orlic, Kajstura et al. 2001; Orlic, Kajstura et al. 2001; Strauer, Brehm et al. 2002), and liver (Avital, Inderbitzin et al. 2001). These studies have been based on the detection of the presence of non-hematopoietic stem cells and endothelial precursor cells in bone marrow (Prockop, Azizi et al. 2000) (Pittenger, Mackay et al. 1999) (Shi, Rafii et al. 1998; Carmeliet and Luttun 2001).
These studies used bone marrow transplant recipient animals in which donor and host cells could be distinguished by genetic markers to show that some fraction of new blood vessel development in the recipients was derived from the donor marrow cells (Carmeliet and Luttun 2001) (Takahashi, Kalka et al. 1999; Murayama, Tepper et al. 2002). While this work definitively demonstrates that marrow contains such cells it has generally been extended to mean that marrow is therefore the only tissue that contains relevant numbers of such cells to the extent that when an investigator detects endothelial precursor cells (EPCs) or marrow stem cells (MSCs) in the circulation it is automatically assumed that these cells are necessarily marrow-derived. Thus, the concept that cell populations from other tissues might represent an alternative or perhaps superior source of therapeutically relevant cell populations is not addressed.
It has been demonstrated that adipose tissue contains a population multipotent stem cells (Huang, Beanes et al. 2002; Mizuno, Zuk et al. 2002) (Zuk, Zhu et al. 2001). Zuk et al. (Zuk et al., (In Press) Human Adipose Tissue Is A Source Of Multipotent Stem Cells, Molecular Biology of the Cell) and others have previously shown that this tissue is a source of endothelial cells (Kern, Knedler et al. 1983; Hutley, Herington et al. 2001) [U.S. Pat. No. 5,372,945 Alchas et al, 1994] though these latter documents did not examine and do not speak in any way to endothelial precursor cells.
Stem cells are the master cells of the body. Stem cells from embryos or embryonic stem cells (ESCs) are know to become many if not all of the cell and tissue types of the body. These early fetal cells not only contain all the genetic information of the individual but also contain the nascent capacity to become any of the 200+ cells and tissues of the body. Ongoing research suggests that these cells have tremendous scientific and clinical potential.
However, ESCs have theoretic limitations to their use. If used clinically they would necessarily be derived from another individual, an embryo. When stem cells or tissues derived from them are transplanted into another person, toxic immune suppressing drugs may be needed by the cell recipient to prevent rejection. In addition, another individual's cells can carry viruses or other rare but significant diseases that can be transmitted to the recipient. Also, ESC-like cells (eg. teratomas) are known to form tumors.
Recently, non-embryonic or adult stem cells have been identified and represent an important potential alternative to the clinical use of ESCs. These cells reside quietly in many if not all tissues, presumably waiting to respond to trauma or other destructive disease processes so that they can heal the injured tissue. Emerging scientific evidence indicates that each individual carries a pool of stem cells that may share with ESCs the ability to become many if not all types of cells and tissues.
Adult stem cell populations have been shown to be present in one or more of skin, muscle, marrow, liver, brain, and adipose tissue. To date proposed application of such cells in tissue engineering involve increasing cell number, purity, and maturity by processes of cell purification and cell culture. These steps are necessary to compensate for the rarity of stem cells in most tissues. For example, mesenchymal stem cell frequency in bone marrow is estimated at between 1 in 100,000 and 1 in 1 million nucleated cells. Similarly, extraction of stem cells from skin involves a complicated series of cell culture steps over several weeks. Use of skeletal muscle-derived stem cells in clinical trials of heart disease employs a two to three week culture phase in which cell number is increased to clinically relevant numbers and cell differentiation into muscle is promoted.
These expansion and differentiation steps may provide increased cell number, purity, and maturity, but they do so at a cost. This cost can include one or more of: loss of cell function due to cell aging, loss of potentially useful non-stem cell populations, delays in potential application of cells to patients, increased monetary cost, and increased risk of contamination of cells with environmental microorganisms during culture. While human data is now becoming available with marrow-derived cells that have not been manipulated but rather used as essentially whole marrow (Horwitz, Prockop et al. 1999; Horwitz, Prockop et al. 2001) (Strauer, Brehm et al. 2002), the clinical benefit derived has been suboptimal, an outcome almost certainly related to the limited cell dose and purity available from marrow.
A number of devices have been developed for harvesting cells from adipose tissue, but these devices can suffer from one or more of inability to optimally accommodate an aspiration device for removal of adipose tissue, lack of partial or full automation from the harvesting of adipose tissue phase through the processing of tissue phases, lack of volume capacity greater than 100 ml of adipose tissue, lack of a partially or completely closed system from the harvesting of adipose tissue phase through the processing of tissue phases, and lack of disposability of components to attenuate concomitant risks of cross-contamination of material from one sample to another.
There is need for alternate approaches in which a population of active cells with increased yield, consistency and/or purity can be prepared rapidly and reliably, and whereby the need for post-extraction manipulation of the cells can be reduced or eliminated. Ideally this cell population would be obtained in a manner that is suitable for their direct placement into a recipient.